Make an object orbit another object indefinitely
So my understanding is that you are attempting to make an object orbit around another one. In order to have this happen, the general workflow is to first make an Empty at the pivot point, parent an object to it, and then animate the Empty. 

Here is how to do it: 


Select the "center" object (the one the moon would orbit around) by clicking on it.
Press ShiftS and select "cursor to selected". That way, when we create the Empty (the point the moon will orbit around), it will be located on the Planet's origin.
Press ShiftA and add an Empty -> Plain Axes.
Select the Moon, then Shift-Click the Plain Axes and press CtrlP, and select "Keep Transform". This will make any transformations applied to the Plain Axes also apply to the Moon.
Now keyframe animate the Plane Axes however you want, and it will animate the Moon as it spins. Maybe add a Cycles Modifier to the animation graph so that it will repeat it forever.


Here is a quick gif that shows this entire process: